This project is concerned with studies of Rocky Mountain spotted fever and other tick-borne rickettsial diseases in the United States regarding ecology, identification, and characterization of the rickettsial agent(s) with their associated vectors. With the collaboration to outside agencies (state health departments, public health laboratories, hospitals, physicians, etc.), source material for comparative studies on the various rickettsial types and information about the distribution of vector species associated with spotted fever in the United States is obtained. This project also considers the cellular and subcellular aspects of interaction between tickborne agents, particularly rickettsiae, and their vectors.